The piercing screams of a severely autistic 7-year-old rang through a Brooklyn courtroom yesterday, as jurors heard a 2005 recording in which a bus matron raged “Shut up!” at the boy and griped, “We got a crazy kid here.”

As a civil trial opened in Brooklyn, P.J. Rossi’s parents finally got their day in court — nearly seven years after their son endured heartless hectoring from bus matron Connie Clark while he bashed his head 80 times against the side of the bus.

The boy’s mom, Lisa Rossi, made the tape on the sly after noting that her son — who cannot speak — was coming home with bumps on his head.

“I put a tape recorder in his backpack so I could find out what was going on,” Rossi said.

What she heard was stomach-turning — her son was called a “knucklehead” and taunted by bus driver Robert Fischetti with offers of cookies and cupcakes.

The taunts led to criminal charges against Clark, legislation calling for increased training for school-bus staffers working with autistic kids — and a lawsuit against the Department of Education and the Atlantic Express bus company. Clark took a no-jail misdemeanor plea.

“P.J. endured 35 minutes of taunting, of mimicking his crying, of saying, ‘You want a cupcake, P.J.?’ ” the family’s lawyer Thomas McManus said. “All the while, P.J. is bashing his head against the side window of bus.”

Lisa Rossi and her husband, Paul, contend their son — now 14 — had his development stunted by the encounter, and said he was denied a properly trained staffer on the bus. They’re seeking unspecified damages.

A city lawyer blamed Atlantic Express, saying Fischetti and Clark were bus company staffers.

But a bus-company lawyer said the city should not have allowed bus matrons to do the job of paraprofessionals.